The invention relates to the field of filter elements for filtering solids from a liquid, and in particular to a screen basket for use in filtering an aqueous fiber solution.
Screening systems are widely used in manufacturing processes to separate larger particles from a liquid/solid suspension. For example, applications for screening systems include processing chemical pulp, mechanical groundwood, bleached or unbleached kraft, old corrugated containers, mixed news, deink stock, waste paper or any other type of fiber.
The system typically receives several thousand gallons per minute of liquid/solid suspension, and separates the larger particles using a pressure screen which typically provides an accept flow (smaller particles) and a reject flow (larger particles). An example of a pressure screen is the Model 400 available from Voith Sulzer, the assignee of the present invention.
Pressure screens often filter the liquid/solid suspension through a slotted or perforated cylindrical screen basket. These prior art screen baskets are relatively expensive, and when the filtering element of the screen basket punctures the pressure screen must be shutdown. The screen basket is then replaced and the pressure screen is brought back on line. The failed screen basket is then generally discarded since repair is too difficult.
The difficulty in repairing the screen basket is primarily due to the relatively complicated structure of the basket. For example, U.S. Pat. Nos. 3,716,144 and 5,255,790 disclose fabricating screen baskets from a plurality of wires secured by welding or brazing to transversely standing support elements. The wires are profiled and suitably spaced to define continuous screening slots communicating with continuous relief slots, the latter being transversed at spaced locations by the support elements.
U.S. Pat. No. 5,513,757 discloses an improved continuous cut slot screen basket having excellent structural integrity and continuous screening slots of uniform width. However, the screen basket has a relatively complex structure and as a result is relatively expensive to manufacture. In addition, if the basket fails it is removed from the pressure screen, discarded and replaced with another screen basket. Because of the structural complexity of the basket, it is too difficult to repair and hence the entire screen basket is discarded.
Therefore, there is a need for a screen basket that can be easily repaired.